Desmond Tutu stepped out of his armoured 4x4 and walked up to the Athamna family house in Beit Hanoun yesterday. Then the South African archbishop stopped and bowed his head in prayer for a minute.

Before him was an alleyway that 18 months ago was filled with grieving relatives and neighbours and soaked in blood. Shrapnel marks scar the walls of the house and those nearby, where a volley of Israeli artillery shells landed in the middle of a residential street in this eastern Gaza town early on November 8 2006. The shelling killed 18 Palestinian civilians, all members of the Athamna extended family, among them 14 women and children.

Waiting for Tutu was Saad Athamna, 55, who embraced the cleric and then quickly broke down in tears as he described how his three sons and two grandchildren were killed. In his hand Athamna held a small fragment of metal shrapnel. "Israel killed my children while I was praying the morning prayer," he said. "We're thankful that some people remember us and don't forget us," added his wife, Hayat.

Tutu spent more than an hour listening, mostly in silence, to the story of one relative after another who described the shelling and horrific injuries, and who pointed out the damage that remains in the house.

The family now lives only on the ground floor, the walls decorated with pictures of the dead. The upper floors of the house are still damaged, including a second-floor room where Tutu was shown chunks of rubble on the floor, a sink smashed in half and a large, round hole in the concrete roof where a shell hit. Two rusting children's bicycles leaned against the wall in another room.

The visit was the long-delayed product of a UN human rights council decision reached days after the incident to send a fact-finding mission to Beit Hanoun. The decision was controversial.

Israel, which has long viewed the council as politicised and biased, refused Tutu a visa, which meant he could not travel to Gaza. Israel said the shelling was due to a "technical failure" in the artillery.

Eventually the Nobel laureate and anti-apartheid campaigner crossed into Gaza on Tuesday from Egypt via the Rafah crossing, which is almost never used for such diplomatic missions but which meant Tutu did not require a visa.

By the time he arrived he found a family of survivors embittered and frustrated. They have received no financial help since the shelling, apart from a monthly stipend from the Palestinian Authority of £50 for each of the 18 dead. Where once there were more than 30 relatives living in the large house, now there are 10. The elder surviving sons moved out and rented apartments elsewhere. "Since that day we've received nothing," said Majdi Athamna, 40, who has moved out.

"How would you feel to walk in the street without your family?" Saad Athamna said to Tutu. "My children were killed and the Palestinian people have no protection." His daughter Ilham, 21, said: "The hardest thing was to see my brothers and sisters cut into pieces on the ground." Others told Tutu how Israeli troops had been in the house a day or two before the shelling, during a major incursion into the town.

As Tutu left the house he said: "We want to say we are quite devastated. This is not something you would want to wish on your worst enemy." He spent the rest of the day taking detailed testimony from witnesses.

In February, the Israeli military said there were no grounds to open a military police investigation or to take legal action against any soldier over the incident. The military said the artillery fire that morning was launched because of "credible and specific intelligence information" and had been aimed 450 metres away from the edge of the town.

They added that the houses were mistakenly hit because of "incorrect range-findings" caused by "a rare and severe failure in the artillery fire control system operated at the time of the incident".